Fiber optical beam delivery device producing selectable intensity profiles

ABSTRACT

An optical beam delivery device is configured to generate, from an optical beam, selectable intensity profiles. The device has a first length of fiber having a first refractive index profile (RIP), and a second length of fiber having second RIP that is different from the first RIP. The second length of fiber includes coaxial confinement regions arranged to confine at least a portion of an adjusted optical beam. The confined portion corresponds to an intensity distribution of different intensity distributions. The intensity distribution is established by a corresponding state of different states of perturbation that is applied to the device such that the confined portion is configured to provide, at an output of the second length of fiber, a selected intensity profile of the selectable intensity profiles.

RELATED APPLICATIONS

This application is a continuation-in-part of each of the followingapplications filed May 26, 2017: U.S. patent application Ser. Nos.15/607,399; 15/607,410; and Ser. No. 15/607,411; and InternationalApplication No. PCT/US2017/034848. Each of these applications claimsbenefit of U.S. Provisional Patent Application No. 62/401,650, filedSep. 29, 2016. All of these applications are incorporated by referenceherein in their entireties.

TECHNICAL FIELD

The technology disclosed herein relates to fiber lasers andfiber-coupled lasers. More particularly, the disclosed technologyrelates to methods, apparatus, and systems for adjusting and maintainingadjusted optical beam characteristics (spot size, divergence profile,spatial profile, or beam shape, or the like or any combination thereof)at an output of a fiber laser or fiber-coupled laser.

BACKGROUND

The use of high-power fiber-coupled lasers continues to gain popularityfor a variety of applications, such as materials processing, cutting,welding, and/or additive manufacturing. These lasers include, forexample, fiber lasers, disk lasers, diode lasers, diode-pumped solidstate lasers, and lamp-pumped solid state lasers. In these systems,optical power is delivered from the laser to a workpiece via an opticalfiber.

Various fiber-coupled laser materials processing tasks require differentbeam characteristics (e.g., spatial profiles and/or divergenceprofiles). For example, cutting thick metal and welding generallyrequire a larger spot size than cutting thin metal. Ideally, the laserbeam properties would be adjustable to enable optimized processing forthese different tasks. Conventionally, users have two choices: (1)Employ a laser system with fixed beam characteristics that can be usedfor different tasks but is not optimal for most of them (i.e., acompromise between performance and flexibility); or (2) Purchase a lasersystem or accessories that offer variable beam characteristics but thatadd significant cost, size, weight, complexity, and perhaps performancedegradation (e.g., optical loss) or reliability degradation (e.g.,reduced robustness or up-time). Currently available laser systemscapable of varying beam characteristics require the use of free-spaceoptics or other complex and expensive add-on mechanisms (e.g., zoomlenses, mirrors, translatable or motorized lenses, combiners, etc.) inorder to vary beam characteristics. No solution exists that provides thedesired adjustability in beam characteristics that minimizes oreliminates reliance on the use of free-space optics or other extracomponents that add significant penalties in terms of cost, complexity,performance, and/or reliability. What is needed is an in-fiber apparatusfor providing varying beam characteristics and shapes that does notrequire or minimizes the use of free-space optics and that can avoidsignificant cost, complexity, performance tradeoffs, and/or reliabilitydegradation.

SUMMARY

This disclosure is summarized by way of the following exampleembodiments. Additional aspects and advantages will be apparent from thedetailed description of embodiments that follows, which proceeds withreference to the accompanying drawings.

Example Embodiment 1

An optical beam delivery device configured to generate, from an opticalbeam, selectable intensity profiles, the optical beam delivery devicecomprising: a first length of fiber having a first refractive indexprofile (RIP), the first RIP enabling, in response to an appliedperturbation, modification of the optical beam to form an adjustedoptical beam, the adjusted optical beam defining, at an output end ofthe first length of fiber, different intensity distributions based ondifferent states of the applied perturbation; and a second length offiber having an input end coupled to the output end of the first lengthof fiber, the second length of fiber formed with coaxial confinementregions defining a second RIP that is different from the first RIP, thecoaxial confinement regions arranged to confine at least a portion ofthe adjusted optical beam, the confined portion corresponding to anintensity distribution of the different intensity distributions, and inwhich the intensity distribution is established by a corresponding stateof the different states of the applied perturbation such that theconfined portion is configured to provide, at an output of the secondlength of fiber, a selected intensity profile of the selectableintensity profiles. In some examples of the device, the selected outputintensity profile is Gaussian, super-Gaussian, flat-top, saddle-shaped,or donut-shaped.

Example Embodiment 2

The optical beam delivery device of the previous example 1, in which theselected intensity profile is a Gaussian intensity profile.

Example Embodiment 3

The optical beam delivery device of the previous example 2, in which thecorresponding state of the different states of the applied perturbationestablishing the Gaussian intensity profile includes an unperturbedstate of the first length of fiber.

Example Embodiment 4

The optical beam delivery device of the previous example 2, in which acentral core of the coaxial confinement regions is configured to providethe confined portion having the Gaussian intensity profile.

Example Embodiment 5

The optical beam delivery device of the previous example 1, in which theselected intensity profile is a super-Gaussian intensity profile.

Example Embodiment 6

The optical beam delivery device of the previous example 1 or 5, inwhich the coaxial confinement regions comprise a central core and anannular region encompassing the central core, and in which thecorresponding state of the different states of the applied perturbationis that which shifts, expands, or simultaneously shifts and expands theoptical beam in forming the adjusted optical beam so that the intensitydistribution which results at the input of the second length of fiberspatially overlaps adjacent portions of the central core and the annularregion.

Example Embodiment 7

The optical beam delivery device of the previous example 1, in which theselected intensity profile is a flat-top intensity profile.

Example Embodiment 8

The optical beam delivery device of the previous example 1, in which theselected intensity profile is a saddle-shaped intensity profile.

Example Embodiment 9

The optical beam delivery device of any one of the previous example 1,5, or 8, in which the coaxial confinement regions comprise a centralcore and an annular region encompassing the central core, and in whichthe intensity distribution spatially overlaps an outer portion of thecentral core and an inner portion of the annular region.

Example Embodiment 10

The optical beam delivery device of the previous example 1, in which theselected intensity profile is a donut-shaped intensity profile.

Example Embodiment 11

The optical beam delivery device of any one of the previous example 1, 8or 10, in which the selected intensity profile includes a local minimumbetween bimodal local maxima.

Example Embodiment 12

A beam shaper system, comprising a laser source to provide an opticalbeam; a variable beam characteristics (VBC) fiber including first andsecond lengths of fiber coupled to each other and having, respectively,first and second refractive index profiles (RIPs) that are differentfrom each other, the first RIP enabling, in response to perturbationapplied to the VBC fiber, modification of the optical beam to form anadjusted optical beam exhibiting at an input of the second length offiber an intensity distribution that is adjustable based on differentstates of the perturbation applied, and the second RIP defined bycoaxial confinement regions arranged to confine at least a portion ofthe adjusted optical beam that corresponds to the intensitydistribution; and a controller operatively coupled to the VBC fiber andconfigured to control the different states of the perturbation so as toestablish different selectable intensity profiles that the confinedportion of the adjusted optical beam is configured to provide at anoutput of the second length of fiber.

Example Embodiment 13

The beam shaper system of the previous example 12, in which one of thedifferent selectable intensity profiles is a Gaussian intensity profile.

Example Embodiment 14

The beam shaper system of the previous example 12, in which one of thedifferent selectable intensity profiles is a super-Gaussian intensityprofile.

Example Embodiment 15

The beam shaper system of the previous example 12, in which one of thedifferent selectable intensity profiles is a saddle-shaped intensityprofile.

Example Embodiment 16

The beam shaper system of the previous example 12, in which one of thedifferent selectable intensity profiles is a donut-shaped intensityprofile.

Example Embodiment 17

A method of generating, from an optical beam, different beam shapesdefined by selectable intensity profiles, comprising: receiving theoptical beam at a variable beam characteristics (VBC) fiber includingfirst and second lengths of fiber coupled to each other and having,respectively, first and second refractive index profiles (RIPs) that aredifferent from each other, the first RIP enabling, in response to aselected state of perturbation applied to the VBC fiber, modification ofthe optical beam to form an adjusted optical beam that is adjustablebased on the selected state of applied perturbation, and the second RIPdefined by coaxial confinement regions arranged to confine at least aportion of the adjusted optical beam; applying a first state ofperturbation to the VBC fiber to establish a first selected intensityprofile at an output end of the second length of fiber; and applying asecond state of perturbation, different from the first state, to the VBCfiber to establish a second selected intensity profile, different fromthe first selected intensity profile, at the output end of the secondlength of fiber.

Example Embodiment 18

The method of the previous example 17, in which the first selectedintensity profile is a generally Gaussian intensity profile, and thesecond intensity profile is a generally super-Gaussian profile.

Example Embodiment 19

The method of the previous example 17, in which the second state ofperturbation is a magnitude of perturbation that is greater than that ofthe first state.

Example Embodiment 20

The method of the previous example 17, in which the first selectedintensity profile is a generally saddle-shaped intensity profile, andthe second intensity profile is a generally donut-shaped intensityprofile.

Further example embodiments: A computer- or machine-readable medium torealize an apparatus, system, or device, or to store instructionsthereon for a processor that, when executing the instructions, performsany example method.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals representlike elements, are incorporated in and constitute a part of thisspecification and, together with the description, explain the advantagesand principles of the presently disclosed technology. In the drawings,

FIG. 1 illustrates an example fiber structure for providing a laser beamhaving variable beam characteristics;

FIG. 2 depicts a cross-sectional view of an example fiber structure fordelivering a beam with variable beam characteristics;

FIG. 3 illustrates an example method of perturbing a fiber structure forproviding a beam having variable beam characteristics;

FIG. 4 is a graph illustrating the calculated spatial profile of thelowest-order mode (LP₀₁) for a first length of a fiber for differentfiber bend radii;

FIG. 5 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis nearly straight;

FIG. 6 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis bent with a radius chosen to preferentially excite a particularconfinement region of a second length of fiber;

FIGS. 7A, 7B, and 7C collectively show a prophetic example of a secondlength of the fiber structure of FIG. 2 receiving at its input end anoptical beam having an intensity distribution (shown in a pictorial viewof FIG. 7A), which is developed by not substantially perturbing thefiber structure such that the second length exhibits at its output end aGaussian intensity distribution (shown in a pictorial view of FIG. 7B)and a corresponding intensity profile (shown in a graph of FIG. 7C);

FIGS. 8A, 8B, and 8C collectively show a prophetic example of a secondlength of the fiber structure of FIG. 2 receiving at its input end anoptical beam having an intensity distribution (shown in a pictorial viewof FIG. 8A), which is developed by a low to intermediate amount ofperturbation applied to the fiber structure such that the second lengthexhibits at its output end a super-Gaussian intensity distribution(shown in a pictorial view of FIG. 8B) and a corresponding intensityprofile (shown in a graph of FIG. 8C) that is adjustable to approach anidealized flat-top intensity profile;

FIGS. 9A, 9B, and 9C collectively show a prophetic example of a secondlength of the fiber structure of FIG. 2 receiving at its input end anoptical beam having an intensity distribution (shown in a pictorial viewof FIG. 9A), which is developed by a further amount of perturbationapplied to the fiber structure such that the second length exhibits atits output end a saddle-shaped intensity distribution (shown in apictorial view of FIG. 9B) and a corresponding intensity profile (shownin a graph of FIG. 9C);

FIGS. 10A, 10B, and 10C collectively show a prophetic example of asecond length of the fiber structure of FIG. 2 receiving at its inputend an optical beam having an intensity distribution (shown in apictorial view of FIG. 10A), which is developed by a still furtheramount of perturbation applied to the fiber structure such that thesecond length exhibits at its output end a donut-shaped intensitydistribution (shown in a pictorial view of FIG. 10B) and a correspondingintensity profile (shown in a graph of FIG. 10C);

FIGS. 11-16 illustrate cross-sectional views of example first lengths offiber for enabling adjustment of beam characteristics in a fiberassembly;

FIGS. 17-19 illustrate cross-sectional views of example second lengthsof fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly;

FIGS. 20 and 21 illustrate cross-sectional views of example secondlengths of fiber for changing a divergence angle of and confining anadjusted beam in a fiber assembly configured to provide variable beamcharacteristics;

FIG. 22A illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and process head;

FIG. 22B illustrates an example a laser system including a fiberassembly configured to provide variable beam characteristics disposedbetween a feeding fiber and process head;

FIG. 23 illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and multiple process fibers;

FIG. 24 illustrates examples of various perturbation assemblies forproviding variable beam characteristics according to various examplesprovided herein;

FIG. 25 illustrates an example process for adjusting and maintainingmodified characteristics of an optical beam;

FIGS. 26-28 are cross-sectional views illustrating example secondlengths of fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly; and

FIG. 29 is a block diagram of a beam shaper configured to generate beamshapes based on selected intensity profiles.

DETAILED DESCRIPTION

As used herein throughout this disclosure and in the claims, thesingular forms “a,” “an,” and “the” include the plural forms unless thecontext clearly dictates otherwise. Additionally, the term “includes”means “comprises.” Further, the term “coupled” does not exclude thepresence of intermediate elements between the coupled items. Also, theterms “modify” and “adjust” are used interchangeably to mean “alter.”

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus are referred to as“lowest,” “best,” “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

Definitions

Definitions of words and terms as used herein:

-   -   1. The term “beam characteristics” refers to one or more of the        following terms used to describe an optical beam. In general,        the beam characteristics of most interest depend on the        specifics of the application or optical system.    -   2. The term “beam diameter” is defined as the distance across        the center of the beam along an axis for which the irradiance        (intensity) equals 1/e² of the maximum irradiance. While        examples disclosed herein generally use beams that propagate in        azimuthally symmetric modes, elliptical or other beam shapes can        be used, and beam diameter can be different along different        axes. Circular beams are characterized by a single beam        diameter. Other beam shapes can have different beam diameters        along different axes.    -   3. The term “spot size” is the radial distance (radius) from the        center point of maximum irradiance to the 1/e² point.    -   4. The term “beam divergence distribution” is the power vs the        full cone angle. This quantity is sometimes called the “angular        distribution” or “NA distribution.”    -   5. The term “beam parameter product” (BPP) of a laser beam is        defined as the product of the beam radius (measured at the beam        waist) and the beam divergence half-angle (measured in the far        field). The units of BPP are typically mm-mrad.    -   6. A “confinement fiber” is defined to be a fiber that possesses        one or more confinement regions, wherein a confinement region        comprises a higher-index region (core region) surrounded by a        lower-index region (cladding region). The RIP of a confinement        fiber may include one or more higher-index regions (core        regions) surrounded by lower-index regions (cladding regions),        wherein light is guided in the higher-index regions. Each        confinement region and each cladding region can have any RIP,        including but not limited to step-index and graded-index. The        confinement regions may or may not be concentric and may be a        variety of shapes such as circular, annular, polygonal, arcuate,        elliptical, or irregular, or the like or any combination        thereof. The confinement regions in a particular confinement        fiber may all have the same shape or may be different shapes.        Moreover, confinement regions may be co-axial or may have offset        axes with respect to one another. Confinement regions may be of        uniform thickness about a central axis in the longitudinal        direction, or the thicknesses may vary about the central axis in        the longitudinal direction.    -   7. The term “intensity distribution” generally refers to optical        intensity as a function of position. When referring to optical        intensity along a line (1D, see e.g., FIGS. 7C, 8C, 9C, and        10C), the specific term “intensity profile” is preferred. When        referring to optical intensity along a plane (2D, see e.g.,        FIGS. 7B, 8B, 9B, and 10B), the more general term “intensity        distribution” is used. In either case, the line or plane is        usually taken perpendicular to the propagation direction of the        light. It is a quantitative property. Furthermore, the term        “beam shape” is used to describe spatial aspects of a profile        (e.g., as in saddle-shaped profiles), but it is also used to        describe spatial aspects of a distribution (e.g., as in        donut-shaped distributions). Skilled persons will appreciate        that, depending on the context, the aforementioned terms are        sometimes used interchangeably. Thus, some additional        qualitative properties of certain beam shapes are shown in the        drawing figures and described in later paragraphs.    -   8. “Luminance” is a photometric measure of the luminous        intensity per unit area of light travelling in a given        direction.    -   9. “M² factor” (also called “beam quality factor” or “beam        propagation factor”) is a dimensionless parameter for        quantifying the beam quality of laser beams, with M²=1 being a        diffraction-limited beam, and larger M² values corresponding to        lower beam quality. M² is equal to the BPP divided by λ/π, where        λ is the wavelength of the beam in microns (if BPP is expressed        in units of mm-mrad).    -   10. The term “numerical aperture” or “NA” of an optical system        is a dimensionless number that characterizes the range of angles        over which the system can accept or emit light.    -   11. The term “optical intensity” is not an official (SI) unit,        but is used to denote incident power per unit area on a surface        or passing through a plane.    -   12. The term “power density” refers to optical power per unit        area, although this is also referred to as “optical intensity.”    -   13. The term “radial beam position” refers to the position of a        beam in a fiber measured with respect to the center of the fiber        core in a direction perpendicular to the fiber axis.    -   14. “Radiance” is the radiation emitted per unit solid angle in        a given direction by a unit area of an optical source (e.g., a        laser). Radiance may be altered by changing the beam intensity        distribution and/or beam divergence profile or distribution. The        ability to vary the radiance profile of a laser beam implies the        ability to vary the BPP.    -   15. The term “refractive-index profile” or “RIP” refers to the        refractive index as a function of position along a line (1D) or        in a plane (2D) perpendicular to the fiber axis. Many fibers are        azimuthally symmetric, in which case the 1D RIP is identical for        any azimuthal angle.    -   16. A “step-index fiber” has a RIP that is flat (refractive        index independent of position) within the fiber core.    -   17. A “graded-index fiber” has a RIP in which the refractive        index decreases with increasing radial position (i.e., with        increasing distance from the center of the fiber core).    -   18. A “parabolic-index fiber” is a specific case of a        graded-index fiber in which the refractive index decreases        quadratically with increasing distance from the center of the        fiber core.

Fiber for Varying Beam Characteristics

Disclosed herein are methods, systems, and apparatus configured toprovide a fiber operable to provide a laser beam having variable beamcharacteristics (VBC) that may reduce cost, complexity, optical loss, orother drawbacks of the conventional methods described above. This VBCfiber is configured to vary a wide variety of optical beamcharacteristics. Such beam characteristics can be controlled using theVBC fiber thus allowing users to tune various beam characteristics tosuit the particular requirements of an extensive variety of laserprocessing applications. For example, a VBC fiber may be used to tunebeam diameter, beam divergence distribution, BPP, intensitydistribution, M² factor, NA, optical intensity, power density, radialbeam position, radiance, spot size, or the like, or any combinationthereof.

In general, the disclosed technology entails coupling a laser beam intoa fiber in which the characteristics of the laser beam in the fiber canbe adjusted by perturbing the laser beam and/or perturbing a firstlength of fiber by any of a variety of methods (e.g., bending the fiberor introducing one or more other perturbations) and fully or partiallymaintaining adjusted beam characteristics in a second length of fiber.The second length of fiber is specially configured to maintain and/orfurther modify the adjusted beam characteristics. In some cases, thesecond length of fiber preserves the adjusted beam characteristicsthrough delivery of the laser beam to its ultimate use (e.g., materialsprocessing). The first and second lengths of fiber may comprise the sameor different fibers.

The disclosed technology is compatible with fiber lasers andfiber-coupled lasers. Fiber-coupled lasers typically deliver an outputvia a delivery fiber having a step-index refractive index profile (RIP),i.e., a flat or constant refractive index within the fiber core. Inreality, the RIP of the delivery fiber may not be perfectly flat,depending on the design of the fiber. Important parameters are the fibercore diameter (d_(core)) and NA. The core diameter is typically in therange of 10-1000 microns (although other values are possible), and theNA is typically in the range of 0.06-0.22 (although other values arepossible). A delivery fiber from the laser may be routed directly to theprocess head or workpiece, or it may be routed to a fiber-to-fibercoupler (FFC) or fiber-to-fiber switch (FFS), which couples the lightfrom the delivery fiber into a process fiber that transmits the beam tothe process head or the workpiece.

Most materials processing tools, especially those at high power (>1 kW),employ multimode (MM) fiber, but some employ single-mode (SM) fiber,which is at the lower end of the d_(core) and NA ranges. The beamcharacteristics from a SM fiber are uniquely determined by the fiberparameters. The beam characteristics from a MM fiber, however, can vary(unit-to-unit and/or as a function of laser power and time), dependingon the beam characteristics from the laser source(s) coupled into thefiber, the launching or splicing conditions into the fiber, the fiberRIP, and the static and dynamic geometry of the fiber (bending, coiling,motion, micro-bending, etc.). For both SM and MM delivery fibers, thebeam characteristics may not be optimum for a given materials processingtask, and it is unlikely to be optimum for a range of tasks, motivatingthe desire to be able to systematically vary the beam characteristics inorder to customize or optimize them for a particular processing task.

In one example, the VBC fiber may have a first length and a secondlength and may be configured to be interposed as an in-fiber devicebetween the delivery fiber and the process head to provide the desiredadjustability of the beam characteristics. To enable adjustment of thebeam, a perturbation device and/or assembly is disposed in closeproximity to and/or coupled with the VBC fiber and is responsible forperturbing the beam in a first length such that the beam'scharacteristics are altered in the first length of fiber, and thealtered characteristics are preserved or further altered as the beampropagates in the second length of fiber. The perturbed beam is launchedinto a second length of the VBC fiber configured to conserve adjustedbeam characteristics. The first and second lengths of fiber may be thesame or different fibers and/or the second length of fiber may comprisea confinement fiber. The beam characteristics that are conserved by thesecond length of VBC fiber may include any of: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity, power density, radial beam position,radiance, spot size, or the like, or any combination thereof.

FIG. 1 illustrates an example VBC fiber 100 for providing a laser beamhaving variable beam characteristics without requiring the use offree-space optics to change the beam characteristics. VBC fiber 100comprises a first length of fiber 104 and a second length of fiber 108.First length of fiber 104 and second length of fiber 108 may be the sameor different fibers and may have the same or different RIPs. The firstlength of fiber 104 and the second length of fiber 108 may be joinedtogether by a splice. First length of fiber 104 and second length offiber 108 may be coupled in other ways, may be spaced apart, or may beconnected via an interposing component such as another length of fiber,free-space optics, glue, index-matching material, or the like or anycombination thereof.

A perturbation device 110 is disposed proximal to and/or envelops aperturbation region 106. Perturbation device 110 may be a device,assembly, in-fiber structure, and/or other feature. Perturbation device110 at least perturbs optical beam 102 in first length of fiber 104 orsecond length of fiber 108 or a combination thereof in order to adjustone or more beam characteristics of optical beam 102. Adjustment of beam102 responsive to perturbation by perturbation device 110 may occur infirst length of fiber 104 or second length of fiber 108 or a combinationthereof. Perturbation region 106 may extend over various widths and mayor may not extend into a portion of second length of fiber 108. As beam102 propagates in VBC fiber 100, perturbation device 110 may physicallyact on VBC fiber 100 to perturb the fiber and adjust the characteristicsof beam 102. Alternatively, perturbation device 110 may act directly onbeam 102 to alter its beam characteristics. Subsequent to beingadjusted, perturbed beam 112 has different beam characteristics fromthose of beam 102, which will be fully or partially conserved in secondlength of fiber 108. In another example, perturbation device 110 neednot be disposed near a splice. Moreover, a splice may not be needed atall, for example VBC fiber 100 may be a single fiber, first length offiber and second length of fiber could be spaced apart, or secured witha small gap (air-spaced or filled with an optical material, such asoptical cement or an index-matching material).

Perturbed beam 112 is launched into second length of fiber 108, whereperturbed beam 112 characteristics are largely maintained or continue toevolve as perturbed beam 112 propagates yielding the adjusted beamcharacteristics at the output of second length of fiber 108. In oneexample, the new beam characteristics may include an adjusted intensitydistribution. In an example, an altered beam intensity distribution willbe conserved in various structurally bounded confinement regions ofsecond length of fiber 108. Thus, the beam intensity distribution may betuned to a desired beam intensity distribution optimized for aparticular laser processing task. In general, the intensity distributionof perturbed beam 112 will evolve as it propagates in the second lengthof fiber 108 to fill the confinement region(s) into which perturbed beam112 is launched responsive to conditions in first length of fiber 104and perturbation caused by perturbation device 110. In addition, theangular distribution may evolve as the beam propagates in the secondfiber, depending on launch conditions and fiber characteristics. Ingeneral, fibers largely preserve the input divergence distribution, butthe distribution can be broadened if the input divergence distributionis narrow and/or if the fiber has irregularities or deliberate featuresthat perturb the divergence distribution. The various confinementregions, perturbations, and fiber features of second length of fiber 108are described in greater detail below. Beams 102 and 112 are conceptualabstractions intended to illustrate how a beam may propagate through aVBC fiber 100 for providing variable beam characteristics and are notintended to closely model the behavior of a particular optical beam.

VBC fiber 100 may be manufactured by a variety of methods including PCVD(Plasma Chemical Vapor Deposition), OVD (Outside Vapor Deposition), VAD(Vapor Axial Deposition), MOCVD (Metal-Organic Chemical VaporDeposition.) and/or DND (Direct Nanoparticle Deposition). VBC fiber 100may comprise a variety of materials. For example, VBC fiber 100 maycomprise SiO₂, SiO₂ doped with GeO₂, germanosilicate, phosphoruspentoxide, phosphosilicate, Al₂O₃, aluminosilicate, or the like or anycombinations thereof. Confinement regions may be bounded by claddingdoped with fluorine, boron, or the like or any combinations thereof.Other dopants may be added to active fibers, including rare-earth ionssuch as Er³⁺ (erbium), Yb³⁺ (ytterbium), Nd³⁺ (neodymium), Tm³⁺(thulium), Ho³⁺ (holmium), or the like or any combination thereof.Confinement regions may be bounded by cladding having a lower index thanthat of the confinement region with fluorine or boron doping.Alternatively, VBC fiber 100 may comprise photonic crystal fibers ormicro-structured fibers.

VBC fiber 100 is suitable for use in any of a variety of fiber, fiberoptic, or fiber laser devices, including continuous wave and pulsedfiber lasers, disk lasers, solid state lasers, or diode lasers (pulserate unlimited except by physical constraints). Furthermore,implementations in a planar waveguide or other types of waveguides andnot just fibers are within the scope of the claimed technology.

FIG. 2 depicts a cross-sectional view of an example VBC fiber 200 foradjusting beam characteristics of an optical beam. In an example, VBCfiber 200 may be a process fiber because it may deliver the beam to aprocess head for material processing. VBC fiber 200 comprises a firstlength of fiber 204 spliced at a junction 206 to a second length offiber 208. A perturbation assembly 210 is disposed proximal to junction206. Perturbation assembly 210 may be any of a variety of devicesconfigured to enable adjustment of the beam characteristics of anoptical beam 202 propagating in VBC fiber 200. In an example,perturbation assembly 210 may be a mandrel and/or another device thatmay provide means of varying the bend radius and/or bend length of VBCfiber 200 near the splice. Other examples of perturbation devices arediscussed below with respect to FIG. 24.

In an example, first length of fiber 204 has a parabolic-index RIP 212as indicated by the left RIP graph. Most of the intensity distributionof beam 202 is concentrated in the center of fiber 204 when fiber 204 isstraight or nearly straight. Second length of fiber 208 is a confinementfiber having RIP 214 as shown in the right RIP graph. Second length offiber 208 includes confinement regions 216, 218, and 220. Confinementregion 216 is a central core surrounded by two annular (or ring-shaped)confinement regions 218 and 220. Layers 222 and 224 are structuralbarriers of lower index material between confinement regions (216, 218and 220), commonly referred to as “cladding” regions. In one example,layers 222 and 224 may comprise rings of fluorosilicate; in someembodiments, the fluorosilicate cladding layers are relatively thin.Other materials may be used as well, and claimed subject matter is notlimited in this regard.

In an example, as beam 202 propagates along VBC fiber 200, perturbationassembly 210 may physically act on fiber 204 and/or beam 202 to adjustits beam characteristics and generate an adjusted beam 226. In thecurrent example, the intensity distribution of beam 202 is modified byperturbation assembly 210. Subsequent to adjustment of beam 202, theintensity distribution of adjusted beam 226 may be concentrated in outerconfinement regions 218 and 220 with relatively little intensity in thecentral confinement region 216. Because each of confinement regions 216,218, and/or 220 is isolated by the thin layers of lower index materialin barrier layers 222 and 224, second length of fiber 208 cansubstantially maintain the adjusted intensity distribution of adjustedbeam 226. Adjusted beam 226 will typically become distributedazimuthally within a given confinement region (see e.g., FIGS. 7B, 8B,9B, and 10B) but will not transition (significantly) between theconfinement regions as it propagates along the second length of fiber208. Thus, the adjusted beam characteristics of adjusted beam 226 arelargely conserved within the isolated confinement regions 216, 218,and/or 220.

In one example, core confinement region 216 and annular confinementregions 218 and 220 may be composed of fused silica glass, and cladding222 and 224 defining the confinement regions may be composed offluorosilicate glass. Other materials may be used to form the variousconfinement regions (216, 218 and 220), including germanosilicate,phosphosilicate, aluminosilicate, or the like, or a combination thereofand claimed subject matter is not so limited. Other materials may beused to form the barrier rings (222 and 224), including fused silica,borosilicate, or the like or a combination thereof, and claimed subjectmatter is not so limited. In other embodiments, the optical fibers orwaveguides include or are composed of various polymers or plastics orcrystalline materials. Generally, the core confinement regions haverefractive indices that are greater than the refractive indices ofadjacent barrier/cladding regions.

In some examples, it may be desirable to increase a number ofconfinement regions in a second length of fiber to increase granularityof beam control over beam displacements for fine-tuning a beam profile.For example, confinement regions may be configured to provide stepwisebeam displacement.

FIG. 3 illustrates an example method of perturbing fiber 200 forproviding variable beam characteristics of an optical beam. Changing thebend radius of a fiber may change the radial beam position, divergenceangle, and/or radiance profile of a beam within the fiber. The bendradius of VBC fiber 200 can be decreased from a first bend radius R₁ toa second bend radius R₂ about splice junction 206 by using a steppedmandrel or cone as perturbation assembly 210. Additionally oralternatively, the engagement length on the mandrel(s) or cone can bevaried. Rollers 250 may be employed to engage VBC fiber 200 acrossperturbation assembly 210. In an example, an amount of engagement ofrollers 250 with fiber 200 has been shown to shift the distribution ofthe intensity profile to the outer confinement regions 218 and 220 offiber 200 with a fixed mandrel radius. There are a variety of othermethods for varying the bend radius of fiber 200, such as using aclamping assembly, flexible tubing, or the like, or a combinationthereof, and claimed subject matter is not limited in this regard. Inanother example, for a particular bend radius the length over which VBCfiber 200 is bent can also vary beam characteristics in a controlled andreproducible way. In examples, changing the bend radius and/or lengthover which the fiber is bent at a particular bend radius also modifiesthe intensity distribution of the beam such that one or more modes maybe shifted radially away from the center of a fiber core.

Maintaining the bend radius of the fibers across junction 206 ensuresthat the adjusted beam characteristics such as radial beam position andradiance profile of optical beam 202 will not return to its unperturbedstate before being launched into second length of fiber 208. Moreover,the adjusted radial beam characteristics, including position, divergenceangle, and/or intensity distribution, of adjusted beam 226 can be variedbased on an extent of decrease in the bend radius and/or the extent ofthe bent length of VBC fiber 200. Thus, specific beam characteristicsmay be obtained using this method.

In the current example, first length of fiber 204 having first RIP 212is spliced at junction 206 to a second length of fiber 208 having asecond RIP 214. However, it is possible to use a single fiber having asingle RIP formed to enable perturbation (e.g., by micro-bending) of thebeam characteristics of beam 202 and to enable conservation of theadjusted beam. Such a RIP may be similar to the RIPs shown in fibersillustrated in FIGS. 17, 18, and/or 19.

FIG. 4 is an example graph 400 illustrating the calculated profile ofthe lowest-order mode (LP₀₁) for a first length of fiber 204 fordifferent fiber bend radii 402, wherein perturbation assembly 210involves bending VBC fiber 200. As the fiber bend radius is decreased,an optical beam propagating in VBC fiber 200 is adjusted such that themode shifts radially away from the center 404 of a VBC fiber 200 core(r=0 micron) toward the core/cladding interface (located at r=100 micronin this example). Higher-order modes (LP_(In)) also shift with bending.Thus, for a straight or nearly straight fiber (very large bend radius),curve 406 for LP₀₁ is centered at or near the center of VBC fiber 200.At a bend radius of about 6 cm, curve 408 for LP₀₁ is shifted to aradial position of about 40 μm from the center 406 of VBC fiber 200. Ata bend radius of about 5 cm, curve 410 for LP₀₁ is shifted to a radialposition about 50 μm from the center 406 of VBC fiber 200. At a bendradius of about 4 cm, curve 412 for LP₀₁ is shifted to a radial positionabout 60 μm from the center 406 of VBC fiber 200. At a bend radius ofabout 3 cm, curve 414 for LP₀₁ is shifted to a radial position about 80μm from the center 406 of VBC fiber 200. At a bend radius of about 2.5cm, a curve 416 for LP₀₁ is shifted to a radial position about 85 μmfrom the center 406 of VBC fiber 200. Note that the shape of the moderemains relatively constant (until it approaches the edge of the core),which is a specific property of a parabolic RIP. Although, this propertymay be desirable in some situations, it is not required for the VBCfunctionality, and other RIPs may be employed.

In an example, if VBC fiber 200 is straightened, LP₀₁ mode will shiftback toward the center of the fiber. Thus, the purpose of second lengthof fiber 208 is to “trap” or confine the adjusted intensity distributionof the beam in a confinement region that is displaced from the center ofthe VBC fiber 200. The splice between fibers 204 and 208 is included inthe bent region, thus the shifted mode profile will be preferentiallylaunched into one of the ring-shaped confinement regions 218 and 220 orbe distributed among the confinement regions. FIGS. 5 and 6 illustratethis effect.

Initially, in second length of fiber 208 shown in the example of FIGS. 5and 6, confinement region 216 has a 100 micron diameter, confinementregion 218 is between 120 micron and 200 micron in diameter, andconfinement region 220 is between 220 micron and 300 micron diameter.Confinement regions 216, 218, and 220 are separated by 10 μm thick ringsof fluorosilicate, providing an NA of 0.22 for the confinement regions.Other inner and outer diameters for the confinement regions, thicknessesof the rings separating the confinement regions, NA values for theconfinement regions, and numbers of confinement regions may be employed.

With the above-noted example dimensions, FIG. 5 illustrates a simulatedexample of a two-dimensional intensity distribution at junction 206within second length of fiber 208 when VBC fiber 200 is nearly straight.A significant portion of LP₀₁ and LP_(In) is within confinement region216 of fiber 208. When VBC fiber 200 is straight (e.g., unperturbed),about 90% of the power is contained within the central confinementregion 216, and about 100% of the power is contained within confinementregions 216 and 218. In contrast, FIG. 6 shows a simulated example of atwo-dimensional intensity distribution of adjusted optical beam 226applied to junction 206 within second length of fiber 208 when VBC fiber200 is bent. A significant portion of LP₀₁ and LP_(In) is withinconfinement region 220 of fiber 208 in response to VBC fiber 200 beingbent with a radius chosen to preferentially excite confinement region220 (the outermost confinement region) of second length of fiber 208.Thus, when fiber 200 is bent to preferentially excite second ringconfinement region 220, nearly 75% of the power is contained withinconfinement region 220, and more than 95% of the power is containedwithin confinement regions 218 and 220. These calculations include LP₀₁and two higher-order modes, which are typical in some 2-4 kW fiberlasers. Specific RIPs, dimensions, and shapes of the confinement regionsfor the two fibers were assumed for the purpose of the thesecalculations, but other RIPs, dimensions, and shapes are possible, andclaimed subject matter is not limited in this regard.

It is clear from FIGS. 5 and 6 that, in the case where perturbationassembly 210 acts on VBC fiber 200 to bend the fiber, the state of thebend radius establishes the spatial overlap of the modal intensitydistribution of the first length of fiber 204 with the differentconfinement regions (216, 218, and 220) of the second length of fiber208. Changing the bend radius can thus change the intensity distributionat the output of the second length of fiber 208, thereby changing thediameter, spot size, or intensity profile of the beam, and thus changingits radiance and BPP value. This adjustment of the spot size may beaccomplished in an all-fiber structure, involving no free-space opticsand consequently may reduce or eliminate the disadvantages of free-spaceoptics discussed above. Such adjustments can also be made with otherperturbation assemblies that alter bend radius, bend length, fibertension, temperature, micro-bending, or other perturbations discussedbelow.

In a typical materials processing system (e.g., a cutting or weldingtool), the output of the process fiber is imaged at or near theworkpiece by the process head. Varying the intensity distribution asshown in FIGS. 5 and 6 thus enables variation of the beam profile at theworkpiece in order to tune and/or optimize the process, as desired. Forexample, FIGS. 7A, 8A, 9A, and 10A show, at junction 206, end views ofsecond length of fiber 208 as different, progressively increasingamounts of perturbation are applied to VBC fiber 200 in response toperturbation assembly 210 acting on VBC fiber 200 to bend the fiber atvarious radii (i.e., decreasing of the bend radius). In these propheticexamples, a beam from a laser source could be launched into an inputfiber (not shown) with a 40 micron core diameter. The input fiber wouldbe spliced to first length of fiber 204. The exact implementationdetails however, will vary depending on the specifics of theapplication. In particular, the spatial profile and divergencedistribution of the output beam and their dependence on bend radius (orother states of applied perturbation) will depend on the specific RIPsemployed, on the splice parameters, and on the characteristics of thelaser source launched into the first fiber.

Optical beam 202, whether adjusted or not, has an intensity distributionin which its area spatially overlaps one or more confinement regions. Aselectable state of perturbation may be applied to moderately shiftoptical beam 202, change its BPP, or modify other beam characteristics(i.e., a change in how the aforementioned area spatially overlaps one ormore confinement regions) so as to generate adjusted optical beam 226.Thus, different beam shapes may be generated based on the amount ofperturbation applied to VBC fiber 200.

FIG. 7A shows a pictorial view of an input end (the end coupled atsplice junction 206 to an output end of a first fiber) of fiber 208.Fiber 208 is shown receiving in its central coaxial confinement region216 an optical beam 202 that is generally unperturbed so as to producefrom it, at the output end of fiber 208, a Gaussian intensitydistribution shown in FIG. 7B, which has a corresponding Gaussianintensity profile 720 shown in FIG. 7C. For example, when VBC fiber 200is straight, a nearly Gaussian input beam shown in FIG. 7A issubstantially confined to confinement region 216 so as to generate thedesired Gaussian intensity distribution at the output. An initial,nominally unperturbed state maintains a generally Gaussian intensityprofile having about 90% of its power contained within the centralconfinement region 216, whereas incremental changes in state may shiftthe generally Gaussian distribution from lower to higher orders of agenerally super-Gaussian distribution. Different states of perturbationmay be used to change the Gaussian center, RMS width, or other Gaussiandistribution parameters of Gaussian intensity profile 720, or togenerate a super-Gaussian beam within central confinement region 216.

Despite excitation of portions of confinement regions from one side atsplice junction 206, the results intensity distributions at the opposingside—shown at the output end in FIGS. 7B, 8B, 9B, and 10B—are nearlysymmetric azimuthally because of scrambling within confinement regionsas the beam propagates within the VBC fiber 200. Although the beam willtypically scramble azimuthally as it propagates, various structures orperturbations (e.g., coils) could be included to facilitate thisprocess.

In some embodiments, it may be desirable to have optical power ofadjusted optical beam 226 divided among confinement regions 216, 218,and/or 220 rather than have it concentrated in a single region. In otherwords, particular confinement regions need not be exclusively excited.For example, as the bend radius is decreased, the intensity distributionat the input shifts to the larger diameters of confinement regions 218and 220 located farther away from confinement region 216—see e.g., thisshift is visible in FIGS. 8A, 9A, and 10A and the resulting output isshown in, respectively, FIGS. 8B, 9B, and 10B. The capability todistribute intensity across one or more confinement regions based on anamount of perturbation advantageously facilitates materials processingapplications optimized by having a flatter (or distributed) beamintensity distribution. Other applications expecting more discreteexcitation of a particular confinement region are also possible usingdifferent fiber RIPs to enable this feature.

FIG. 8A depicts the intensity distribution when the bend radius of VBCfiber 200 is chosen to shift the intensity distribution betweenconfinement regions 216 and 218. In one example, the selected amount ofapplied perturbation is that which simultaneously shifts and expandsoptical beam 202 in forming the adjusted optical beam 226 so the area ofits intensity distribution spatially overlaps the adjacent confinementregions. Thus, the input end of fiber 208 receives adjusted optical beam226 in adjacent portions (e.g., neighboring portions optionallyseparated by lower-index cladding) of its central coaxial confinementregion 216 and middle confinement region 218 so as to produce an outputoptical beam having a generally super-Gaussian intensity distributionshown in FIG. 8B, which has a corresponding super-Gaussian intensityprofile 820 shown in FIG. 8C.

In some embodiments, the aforementioned shift and expansion of opticalbeam 202 causes adjusted optical beam 226 to possess non-zeroellipticity (this phenomena is also simulated as adjusted optical beam226 of FIG. 6.), which facilitates a more even intensity distributionacross confinement regions, resulting in a relatively flat top of arelatively high-order super-Gaussian intensity profile 824. In contrast,less perturbation may be employed to generate a relatively low-ordersuper-Gaussian intensity profile 826. Low-order super-Gaussian intensityprofile 826 is formed, in some embodiments, by applying lessperturbation so as to concentrate more intensity in central coaxialconfinement region(s). Conversely, it should be readily appreciated thathigh-order super-Gaussian intensity profile 824 may approach a flat-top(i.e., a top-hat, for circular beams) intensity profile 830.

Skilled persons will appreciate that the higher the order of asuper-Gaussian profile, the sharper its corners become as it eventuallyapproximates an ideal flat-top. In practice, however, a flat-top profilemaintains at least some rounding in its corners and is typicallyapproximated as a high-order super-Gaussian profile rather than astrictly rectangular profile. Accordingly, a super-Gaussian beam profilehaving a substantially flat-top and Gaussian fall-off is more generallyrepresented by the following equation:

${l(r)} = {l_{p}e^{({- {(\frac{r}{w})}^{2\; n}})}}$

where n is the order, r represents radial position, and I_(p) is peakintensity (on the beam axis) of a Gaussian beam having a Gaussian beamradius w.

Compared to the example of FIG. 8A, the example of FIG. 9A shows greaterradial shift and less ellipticity, and thereby places more intensityaway from region 216 and into region 218. As with the previous examples,the optimal amount of shift or ellipticity may be determinedempirically, on an application-specific basis. For some applications,the bend radius may be further reduced and chosen to shift the intensitydistribution more outward to confinement region 218 and confinementregion 220, leaving less power density in the center and therebyapproximating at the output a saddle-shaped distribution shown in FIG.9B, which has a corresponding saddle-shaped intensity profile 920 shownin FIG. 9C. Profile 920 is generally defined by a bimodal shape thatincludes two local maxima 930 and a local minimum 940 therebetween. Insome embodiments, the local minimum may reach about zero intensity(which would be called a “donut” beam), whereas other embodimentsmaintain residual intensity at the local minimum.

FIG. 10A shows another pictorial view of the input end of fiber 208primarily receiving in its outer coaxial confinement region 220 adjustedoptical beam 226 so as to produce from it an output optical beam havinga so-called donut mode shown in FIG. 10B, which has a correspondingintensity profile 1020 shown in FIG. 10C. In contrast to the previousexamples, adjusted optical beam 226 also has a smaller diameter so as toconcentrate intensity in outer coaxial confinement region 220. Thesmaller diameter is achieved, for example, using a RIP of a first fiberthat is different from the RIP used in connection the previous examplesshown in FIGS. 7B, 8B, and 9B.

Skilled persons will appreciate that the idealized graphs in FIGS. 7C,8C, 9C, and 10C show smooth transitions. In practice, however, claddingbetween confinement regions introduces minor disruptions in intensity.These disruptions are, however, not so significant to fundamentallyalter the character of selected beam shapes. In other words, a saddleshape, for example, need not possess a perfectly smooth bimodal profileto still serve its intended purpose.

Different fiber parameters from those shown in FIG. 2 may be used andstill be within the scope of the claimed subject matter. Specifically,different RIPs and core sizes and shapes may be used to facilitatecompatibility with different input beam profiles and to enable differentoutput beam characteristics. Example RIPs for the first length of fiber,in addition to the parabolic-index profile shown in FIG. 2, includeother graded-index profiles, step-index, pedestal designs (i.e., nestedcores with progressively lower refractive indices with increasingdistance from the center of the fiber), and designs with nested coreswith the same refractive index value but with various NA values for thecentral core and the surrounding rings. Example RIPs for the secondlength of fiber, in addition to the profile shown in FIG. 2, includeconfinement fibers with different numbers of confinement regions,non-uniform confinement-region thicknesses, different and/or non-uniformvalues for the thicknesses of the rings surrounding the confinementregions, different and/or non-uniform NA values for the confinementregions, different refractive-index values for the high-index andlow-index portions of the RIP, non-circular confinement regions (such aselliptical, oval, polygonal, square, rectangular, or combinationsthereof), as well as other designs as discussed in further detail withrespect to FIGS. 26-28. Furthermore, VBC fiber 200 and other examples ofa VBC fiber described herein are not restricted to use of two fibers. Insome examples, implementation may include use of one fiber or more thantwo fibers. In some cases, the fiber(s) may not be axially uniform; forexample, they could include fiber Bragg gratings or long-periodgratings, or the diameter could vary along the length of the fiber. Inaddition, the fibers do not have to be azimuthally symmetric, e.g., thecore(s) could have square or polygonal shapes. Various fiber coatings(buffers) may be employed, including high-index or index-matchedcoatings (which strip light at the glass-polymer interface) andlow-index coatings (which guide light by total internal reflection atthe glass-polymer interface). In some examples, multiple fiber coatingsmay be used on VBC fiber 200.

FIGS. 11-16 illustrate cross-sectional views of examples of firstlengths of fiber for enabling adjustment of beam characteristics in aVBC fiber responsive to perturbation of an optical beam propagating inthe first lengths of fiber. Some examples of beam characteristics thatmay be adjusted in the first length of fiber are: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity profile, power density profile, radialbeam position, radiance, spot size, or the like, or any combinationthereof. The first lengths of fiber depicted in FIGS. 11-16 anddescribed below are merely examples and do not provide an exhaustiverecitation of the variety of first lengths of fiber that may be utilizedto enable adjustment of beam characteristics in a VBC fiber assembly.Selection of materials, appropriate RIPs, and other variables for thefirst lengths of fiber illustrated in FIGS. 11-16 at least depend on adesired beam output. A wide variety of fiber variables are contemplatedand are within the scope of the claimed subject matter. Thus, claimedsubject matter is not limited by examples provided herein.

In FIG. 11 first length of fiber 1100 comprises a step-index profile1102. FIG. 12 illustrates a first length of fiber 1200 comprising a“pedestal RIP” (i.e., a core comprising a step-index region surroundedby a larger step-index region) 1202. FIG. 13 illustrates a first lengthof fiber 1300 comprising a multiple-pedestal RIP 1302.

FIG. 14A illustrates a first length of fiber 1400 comprising agraded-index profile 1418 surrounded by a down-doped region 1404. Whenthe fiber 1400 is perturbed, modes may shift radially outward in fiber1400 (e.g., during bending of fiber 1400). Graded-index profile 1402 maybe designed to promote maintenance or even compression of modal shape.This design may promote adjustment of a beam propagating in fiber 1400to generate a beam having a beam intensity distribution concentrated inan outer perimeter of the fiber (i.e., in a portion of the fiber corethat is displaced from the fiber axis). As described above, when theadjusted beam is coupled into a second length of fiber havingconfinement regions, the intensity distribution of the adjusted beam maybe trapped in the outermost confinement region, providing a donut shapedintensity distribution. A beam spot having a narrow outer confinementregion may be useful to enable certain material processing actions.

FIG. 14B illustrates a first length of fiber 1406 comprising agraded-index profile 1414 surrounded by a down-doped region 1408 similarto that of fiber 1400. However, fiber 1406 includes a divergencestructure 1410 (a lower-index region) as can be seen in profile 1412.The divergence structure 1410 is an area of material with a lowerrefractive index than that of the surrounding core. As the beam islaunched into first length of fiber 1406, refraction from divergencestructure 1410 causes the beam divergence to increase in first length offiber 1406. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure 1410 and themagnitude of the index difference between the divergence structure 1410and the core material. Divergence structure 1410 can have a variety ofshapes, depending on the input divergence distribution and desiredoutput divergence distribution. In an example, divergence structure 1410has a triangular or graded index shape.

FIG. 15 illustrates a first length of fiber 1500 comprising aparabolic-index central region 1502 surrounded by a constant-indexregion 1504. Between the constant-index region 1504 and theparabolic-index central region 1502 is a lower-index annular layer (orlower-index ring or annulus) 1506 surrounding the parabolic-indexcentral region 1502. The lower-index annulus 1506 helps guide a beampropagating in fiber 1500. When the propagating beam is perturbed, modesshift radially outward in fiber 1500 (e.g., during bending of fiber1500). As one or more modes shift radially outward, parabolic-indexregion 1502 promotes retention of modal shape. When the modes reach theconstant-index region 1504 at outer portions of a RIP 1510, they will becompressed against the lower-index ring 1506, which (in comparison tothe first fiber RIP shown in FIGS. 14A and 14B) may cause preferentialexcitation of the outermost confinement region in the second fiber. Inone implementation, this fiber design works with a confinement fiberhaving a central step-index core and a single annular core. Theparabolic-index portion 1502 of the RIP 1510 overlaps with the centralstep-index core of the confinement fiber. The constant-index portion1504 overlaps with the annular core of the confinement fiber. Theconstant-index portion 1504 of the first fiber is intended to make iteasier to move the beam into overlap with the annular core by bending.This fiber design also works with other designs of the confinementfiber.

FIG. 16 illustrates a first length of fiber 1600 comprising guidingregions 1604, 1606, 1608, and 1616 bounded by lower-index layers 1610,1612, and 1614 where the indexes of the lower-index layers 1610, 1612,and 1614 are stepped or, more generally, do not all have the same value.The stepped-index layers may serve to bound the beam intensity tocertain guiding regions (1604, 1606, 1608, and 1616) when theperturbation assembly 210 (see FIG. 2) acts on the fiber 1600. In thisway, adjusted beam light may be trapped in the guiding regions over arange of perturbation actions (such as over a range of bend radii, arange of bend lengths, a range of micro-bending pressures, and/or arange of acousto-optical signals), allowing for a certain degree ofperturbation tolerance before a beam intensity distribution is shiftedto a more distant radial position in fiber 1600. Thus, variation in beamcharacteristics may be controlled in a step-wise fashion. The radialwidths of the guiding regions 1604, 1606, 1608, and 1616 may be adjustedto achieve a desired ring width, as may be required by an application.Also, a guiding region can have a thicker radial width to facilitatetrapping of a larger fraction of the incoming beam profile if desired.Region 1606 is an example of such a design.

FIGS. 17-21 depict examples of fibers configured to enable maintenanceand/or confinement of adjusted beam characteristics in the second lengthof fiber (e.g., fiber 208). These fiber designs are referred to as“ring-shaped confinement fibers” because they contain a central coresurrounded by annular or ring-shaped cores. These designs are merelyexamples and not an exhaustive recitation of the variety of fiber RIPsthat may be used to enable maintenance and/or confinement of adjustedbeam characteristics within a fiber. Thus, claimed subject matter is notlimited to the examples provided herein. Moreover, any of the firstlengths of fiber described above with respect to FIGS. 11-16 may becombined with any of the second length of fiber described FIGS. 17-21.

FIG. 17 illustrates a cross-sectional view of an example second lengthof fiber for maintaining and/or confining adjusted beam characteristicsin a VBC fiber assembly. As the perturbed beam is coupled from a firstlength of fiber to a second length of fiber 1700, the second length offiber 1700 may maintain at least a portion of the beam characteristicsadjusted in response to perturbation in the first length of fiber withinone or more of confinement regions 1704, 1706, and/or 1708. Fiber 1700has a RIP 1702. Each of confinement regions 1704, 1706, and/or 1708 isbounded by a lower index layer 1710 and/or 1712. This design enablessecond length of fiber 1700 to maintain the adjusted beamcharacteristics. As a result, a beam output by fiber 1700 willsubstantially maintain the received adjusted beam as modified in thefirst length of fiber giving the output beam adjusted beamcharacteristics, which may be customized to a processing task or otherapplication.

Similarly, FIG. 18 depicts a cross-sectional view of an example secondlength of fiber 1800 for maintaining and/or confining beamcharacteristics adjusted in response to perturbation in the first lengthof fiber in a VBC fiber assembly. Fiber 1800 has a RIP 1802. However,confinement regions 1808, 1810, and/or 1812 have different thicknessesfrom the thicknesses of confinement regions 1704, 1706, and 1708. Eachof confinement regions 1808, 1810, and/or 1812 is bounded by a lowerindex layer 1804 and/or 1806. Varying the thicknesses of the confinementregions (and/or barrier regions) enables tailoring or optimization of aconfined adjusted radiance profile by selecting particular radialpositions within which to confine an adjusted beam.

FIG. 19 depicts a cross-sectional view of an example second length offiber 1900 having a RIP 1902 for maintaining and/or confining anadjusted beam in a VBC fiber assembly configured to provide variablebeam characteristics. In this example, the number and thicknesses ofconfinement regions 1904, 1906, 1908, and 1910 are different from thoseof fiber 1700 and 1800; and the barrier layers 1912, 1914, and 1916 areof varied thicknesses as well. Furthermore, confinement regions 1904,1906, 1908, and 1910 have different indexes of refraction; and barrierlayers 1912, 1914, and 1916 have different indexes of refraction aswell. This design may further enable a more granular or optimizedtailoring of the confinement and/or maintenance of an adjusted beamradiance to particular radial locations within fiber 1900. As theperturbed beam is launched from a first length of fiber to second lengthof fiber 1900, the modified beam characteristics of the beam (having anadjusted intensity distribution, radial position, and/or divergenceangle, or the like, or a combination thereof) is confined within aspecific radius by one or more of confinement regions 1904, 1906, 1908,and/or 1910 of second length of fiber 1900.

As noted previously, the divergence angle of a beam may be conserved oradjusted and then conserved in the second length of fiber. There are avariety of methods to change the divergence angle of a beam. Thefollowing are examples of fibers configured to enable adjustment of thedivergence angle of a beam propagating from a first length of fiber to asecond length of fiber in a fiber assembly for varying beamcharacteristics. However, these are merely examples and not anexhaustive recitation of the variety of methods that may be used toenable adjustment of divergence of a beam. Thus, claimed subject matteris not limited to the examples provided herein.

FIG. 20 depicts a cross-sectional view of an example second length offiber 2000 having a RIP 2002 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. In this example, second length of fiber 2000is similar to the previously described second lengths of fiber and formsa portion of the VBC fiber assembly for delivering variable beamcharacteristics as discussed above. There are three confinement regions2004, 2006, and 2008 and three barrier layers 2010, 2012, and 2016.Second length of fiber 2000 also has a divergence structure 2014situated within the confinement region 2006. The divergence structure2014 is an area of material with a lower refractive index than that ofthe surrounding confinement region. As the beam is launched into secondlength of fiber 2000, refraction from divergence structure 2014 causesthe beam divergence to increase in second length of fiber 2000. Theamount of increased divergence depends on the amount of spatial overlapof the beam with the divergence structure 2014 and the magnitude of theindex difference between the divergence structure 2014 and the corematerial. By adjusting the radial position of the beam near the launchpoint into the second length of fiber 2000, the divergence distributionmay be varied. The adjusted divergence of the beam is conserved in fiber2000, which is configured to deliver the adjusted beam to the processhead, another optical system (e.g., fiber-to-fiber coupler orfiber-to-fiber switch), the workpiece, or the like, or a combinationthereof. In an example, divergence structure 2014 may have an index dipof about 10⁻⁵-3×10⁻² with respect to the surrounding material. Othervalues of the index dip may be employed within the scope of thisdisclosure, and claimed subject matter is not so limited.

FIG. 21 depicts a cross-sectional view of an example second length offiber 2100 having a RIP 2102 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. Second length of fiber 2100 forms a portionof a VBC fiber assembly for delivering a beam having variablecharacteristics. In this example, there are three confinement regions2104, 2106, and 2108 and three barrier layers 2110, 2112, and 2116.Second length of fiber 2100 also has a plurality of divergencestructures 2114 and 2118. The divergence structures 2114 and 2118 areareas of graded lower index material. As the beam is launched from thefirst length fiber into second length of fiber 2100, refraction fromdivergence structures 2114 and 2118 causes the beam divergence toincrease. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure and themagnitude of the index difference between the divergence structure 2114and/or 2118 and the surrounding core material of confinement regions2106 and 2104 respectively. By adjusting the radial position of the beamnear the launch point into the second length of fiber 2100, thedivergence distribution may be varied. The design shown in FIG. 21allows the intensity distribution and the divergence distribution to bevaried somewhat independently by selecting both a particular confinementregion and the divergence distribution within that confinement region(because each confinement region may include a divergence structure).The adjusted divergence of the beam is conserved in fiber 2100, which isconfigured to deliver the adjusted beam to the process head, anotheroptical system, or the workpiece. Forming the divergence structures 2114and 2118 with a graded or non-constant index enables tuning of thedivergence profile of the beam propagating in fiber 2100. An adjustedbeam characteristic such as a radiance profile and/or divergence profilemay be conserved as it is delivered to a process head by the secondfiber. Alternatively, an adjusted beam characteristic such as a radianceprofile and/or divergence profile may be conserved or further adjustedas it is routed by the second fiber through a fiber-to-fiber coupler(FFC) and/or fiber-to-fiber switch (FFS) and to a process fiber, whichdelivers the beam to the process head or the workpiece.

FIGS. 26-28 are cross-sectional views illustrating examples of fibersand fiber RIPs configured to enable maintenance and/or confinement ofadjusted beam characteristics of a beam propagating in an azimuthallyasymmetric second length of fiber, wherein the beam characteristics areadjusted responsive to perturbation of a first length of fiber coupledto the second length of fiber and/or perturbation of the beam by aperturbation device 110. These azimuthally asymmetric designs are merelyexamples and are not an exhaustive recitation of the variety of fiberRIPs that may be used to enable maintenance and/or confinement ofadjusted beam characteristics within an azimuthally asymmetric fiber.Thus, claimed subject matter is not limited to the examples providedherein. Moreover, any of a variety of first lengths of fiber (e.g., likethose described above) may be combined with any azimuthally asymmetricsecond length of fiber (e.g., like those described in FIGS. 26-28).

FIG. 26 illustrates RIPs at various azimuthal angles of a cross-sectionthrough an elliptical fiber 2600. At a first azimuthal angle 2602, fiber2600 has a first RIP 2604. At a second azimuthal angle 2606 that isrotated 45° from first azimuthal angle 2602, fiber 2600 has a second RIP2608. At a third azimuthal angle 2610 that is rotated another 45° fromsecond azimuthal angle 2606, fiber 2600 has a third RIP 2612. First,second, and third RIPs 2604, 2608, and 2612 are all different.

FIG. 27 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a multicore fiber 2700. At a first azimuthal angle 2702, fiber2700 has a first RIP 2704. At a second azimuthal angle 2706, fiber 2700has a second RIP 2708. First and second RIPs 2704 and 2708 aredifferent. In an example, perturbation device 110 may act in multipleplanes in order to launch the adjusted beam into different regions of anazimuthally asymmetric second fiber.

FIG. 28 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a fiber 2800 having at least one crescent shaped core. In somecases, the corners of the crescent may be rounded, flattened, orotherwise shaped, which may minimize optical loss. At a first azimuthalangle 2802, fiber 2800 has a first RIP 2804. At a second azimuthal angle2806, fiber 2800 has a second RIP 2808. First and second RIPs 2804 and2808 are different.

FIG. 22A illustrates an example of a laser system 2200 including a VBCfiber assembly 2202 configured to provide variable beam characteristics.VBC fiber assembly 2202 comprises a first length of fiber 104, a secondlength of fiber 108, and a perturbation device 110. VBC fiber assembly2202 is disposed between feeding fiber 2212 (i.e., the output fiber fromthe laser source) and VBC delivery fiber 2240. VBC delivery fiber 2240may comprise second length of fiber 108 or an extension of second lengthof fiber 108 that modifies, maintains, and/or confines adjusted beamcharacteristics. Beam 2210 is coupled into VBC fiber assembly 2202 viafeeding fiber 2212. Fiber assembly 2202 is configured to vary thecharacteristics of beam 2210 in accordance with the various examplesdescribed above. The output of fiber assembly 2202 is adjusted beam2214, which is coupled into VBC delivery fiber 2240. VBC delivery fiber2240 delivers adjusted beam 2214 to a free-space optics assembly 2208,which then couples beam 2214 into a process fiber 2204. Adjusted beam2214 is then delivered to process head 2206 by process fiber 2204. Theprocess head can include guided wave optics (such as fibers and fibercoupler), free space optics (such as lenses, mirrors, optical filters,diffraction gratings), and/or beam scan assemblies (such as galvanometerscanners, polygonal mirror scanners, or other scanning systems) that areused to shape the beam 2214 and deliver the shaped beam to a workpiece.

In laser system 2200, one or more of the free-space optics of assembly2208 may be disposed in an FFC or other beam coupler 2216 to perform avariety of optical manipulations of an adjusted beam 2214 (representedin FIG. 22A with different dashing from that of beam 2210). For example,free-space optics assembly 2208 may preserve the adjusted beamcharacteristics of beam 2214. Process fiber 2204 may have the same RIPas VBC delivery fiber 2240. Thus, the adjusted beam characteristics ofadjusted beam 2214 may be preserved all the way to process head 2206.Process fiber 2204 may comprise a RIP similar to any of the secondlengths of fiber described above, including confinement regions.

Alternatively, as illustrated in FIG. 22B, free-space optics assembly2208 may change the adjusted beam characteristics of beam 2214 by, forexample, increasing or decreasing the divergence and/or the spot size ofbeam 2214 (e.g., by magnifying or demagnifying beam 2214) and/orotherwise further modifying adjusted beam 2214. Furthermore, processfiber 2204 may have a different RIP than VBC delivery fiber 2240.Accordingly, the RIP of process fiber 2204 may be selected to preserveadditional adjustment of adjusted beam 2214 made by the free-spaceoptics of assembly 2208 to generate a twice adjusted beam 2224(represented in FIG. 22B with different dashing from that of beam 2214).

FIG. 23 illustrates an example of a laser system 2300 including VBCfiber assembly 2302 disposed between a feeding fiber 2312 and a VBCdelivery fiber 2340. During operation, a beam 2310 is coupled into VBCfiber assembly 2302 via feeding fiber 2312. Fiber assembly 2302 includesa first length of fiber 104, a second length of fiber 108, and aperturbation device 110 and is configured to vary characteristics ofbeam 2310 in accordance with the various examples described above. Fiberassembly 2302 generates an adjusted beam 2314 output by VBC deliveryfiber 2340. VBC delivery fiber 2340 comprises a second length of fiber108 of fiber for modifying, maintaining, and/or confining adjusted beamcharacteristics in a fiber assembly 2302 in accordance with the variousexamples described above (see FIGS. 17-21, for example). VBC deliveryfiber 2340 couples adjusted beam 2314 into a beam switch (FFS) 2332,which then couples its various output beams to one or more of multipleprocess fibers 2304, 2320, and 2322. Process fibers 2304, 2320, and 2322deliver adjusted beams 2314, 2328, and 2330 to respective process heads2306, 2324, and 2326.

In an example, beam switch 2332 includes one or more sets of free-spaceoptics 2308, 2316, and 2318 configured to perform a variety of opticalmanipulations of adjusted beam 2314. Free-space optics 2308, 2316, and2318 may preserve or vary adjusted beam characteristics of beam 2314.Thus, adjusted beam 2314 may be maintained by the free-space optics oradjusted further. Process fibers 2304, 2320, and 2322 may have the sameor a different RIP as that of VBC delivery fiber 2340, depending onwhether it is desirable to preserve or further modify a beam passingfrom the free-space optics assemblies 2308, 2316, and 2318 to respectiveprocess fibers 2304, 2320, and 2322. In other examples, one or more beamportions of beam 2310 are coupled to a workpiece without adjustment, ordifferent beam portions are coupled to respective VBC fiber assembliesso that beam portions associated with a plurality of beamcharacteristics can be provided for simultaneous workpiece processing.Alternatively, beam 2310 can be switched to one or more of a set of VBCfiber assemblies.

Routing adjusted beam 2314 through any of free-space optics assemblies2308, 2316, and 2318 enables delivery of a variety of additionallyadjusted beams to process heads 2206, 2324, and 2326. Therefore, lasersystem 2300 provides additional degrees of freedom for varying thecharacteristics of a beam, as well as switching the beam between processheads (“time sharing”) and/or delivering the beam to multiple processheads simultaneously (“power sharing”).

For example, free-space optics in beam switch 2332 may direct adjustedbeam 2314 to free-space optics assembly 2316 configured to preserve theadjusted characteristics of beam 2314. Process fiber 2304 may have thesame RIP as that of VBC delivery fiber 2340. Thus, the beam delivered toprocess head 2306 will be a preserved adjusted beam 2314.

In another example, beam switch 2332 may direct adjusted beam 2314 tofree-space optics assembly 2318 configured to preserve the adjustedcharacteristics of adjusted beam 2314. Process fiber 2320 may have adifferent RIP from that of VBC delivery fiber 2340 and may be configuredwith divergence altering structures as described with respect to FIGS.20 and 21 to provide additional adjustments to the divergencedistribution of beam 2314. Thus, the beam delivered to process head 2324will be a twice adjusted beam 2328 having a different beam divergenceprofile from that of adjusted beam 2314.

Process fibers 2304, 2320, and/or 2322 may comprise a RIP similar to anyof the second lengths of fiber described above, including confinementregions or a wide variety of other RIPs, and claimed subject matter isnot limited in this regard.

In yet another example, free-space optics switch 2332 may directadjusted beam 2314 to free-space optics assembly 2308 configured tochange the beam characteristics of adjusted beam 2314. Process fiber2322 may have a different RIP from that of VBC delivery fiber 2340 andmay be configured to preserve (or alternatively further modify) the newfurther adjusted characteristics of beam 2314. Thus, the beam deliveredto process head 2326 will be a twice adjusted beam 2330 having differentbeam characteristics (due to the adjusted divergence profile and/orintensity profile) from those of adjusted beam 2314.

In FIGS. 22A, 22B, and 23, the optics in the FFC or FFS may adjust thespatial profile and/or divergence profile by magnifying or demagnifyingthe beam 2214 before launching into the process fiber. They may alsoadjust the spatial profile and/or divergence profile via other opticaltransformations. They may also adjust the launch position into theprocess fiber. These methods may be used alone or in combination.

FIGS. 22A, 22B, and 23 merely provide examples of combinations ofadjustments to beam characteristics using free-space optics and variouscombinations of fiber RIPs to preserve or modify adjusted beams 2214 and2314. The examples provided above are not exhaustive and are meant forillustrative purposes only. Thus, claimed subject matter is not limitedin this regard.

FIG. 24 illustrates various examples of perturbation devices, assembliesor methods (for simplicity referred to collectively herein as“perturbation device 110”) for perturbing a VBC fiber 200 and/or anoptical beam propagating in VBC fiber 200 according to various examplesprovided herein. Perturbation device 110 may be any of a variety ofdevices, methods, and/or assemblies configured to enable adjustment ofbeam characteristics of a beam propagating in VBC fiber 200 in responseto application of one or more of various states of perturbation. Someexamples of various states of perturbation that may be applied to VBCfiber 200 include, but are not limited to, amount or direction ofbending, lateral mechanical stress, acoustic wave oscillation-inducedmechanical pressure, temperature variation, piezo-electric transducerdisplacement, and varying periodicity or amplitude of refractivegrating. A variation in one or more states establishes a different stateof perturbation. To vary one or more of these states, perturbationdevice 110 may be a mandrel 2402, a micro-bend 2404 in the VBC fiber,flexible tubing 2406, an acousto-optic transducer 2408, a thermal device2410, a piezo-electric device 2412, a grating 2414, a clamp 2416 (orother fastener), or the like, or any combination thereof. These aremerely examples of perturbation devices 100 and not an exhaustivelisting of perturbation devices 100, and claimed subject matter is notlimited in this regard.

Mandrel 2402 may be used to perturb VBC fiber 200 by providing a formabout which VBC fiber 200 may be bent. As discussed above, reducing thebend radius of VBC fiber 200 moves the intensity distribution of thebeam radially outward. In some examples, mandrel 2402 may be stepped orconically shaped to provide discrete bend radii levels. Alternatively,mandrel 2402 may comprise a cone shape without steps to providecontinuous bend radii for more granular control of the bend radius. Theradius of curvature of mandrel 2402 may be constant (e.g., a cylindricalform) or non-constant (e.g., an oval-shaped form). Similarly, flexibletubing 2406, clamps 2416 (or other varieties of fasteners), or rollers250 may be used to guide and control the bending of VBC fiber 200 aboutmandrel 2402. Furthermore, changing the length over which the fiber isbent at a particular bend radius also may modify the intensitydistribution of the beam. VBC fiber 200 and mandrel 2402 may beconfigured to change the intensity distribution within the first fiberpredictably (e.g., in proportion to the length over which the fiber isbent and/or the bend radius). Rollers 250 may move up and down along atrack 2442 on a platform 2434 to change the bend radius of VBC fiber200.

Clamps 2416 (or other fasteners) may be used to guide and control thebending of VBC fiber 200 with or without a mandrel 2402. Clamps 2416 maymove up and down along a track 2442 or a platform 2446. Clamps 2416 mayalso swivel to change bend radius, tension, or direction of VBC fiber200. A controller 2448 may control the movement of clamps 2416.

In another example, perturbation device 110 may be flexible tubing 2406and may guide bending of VBC fiber 200 with or without a mandrel 2402.Flexible tubing 2406 may encase VBC fiber 200. Tubing 2406 may be madeof a variety of materials and may be manipulated using piezoelectrictransducers controlled by a controller 2444. In another example, clampsor other fasteners may be used to move flexible tubing 2406.

Micro-bend 2404 in VBC fiber is a local perturbation caused by lateralmechanical stress on the fiber. Micro-bending can cause mode couplingand/or transitions from one confinement region to another confinementregion within a fiber, resulting in varied beam characteristics of thebeam propagating in a VBC fiber 200. Mechanical stress may be applied byan actuator 2436 that is controlled by controller 2440. However, this ismerely an example of a method for inducing mechanical stress in fiber200 and claimed subject matter is not limited in this regard.

Acousto-optic transducer (AOT) 2408 may be used to induce perturbationof a beam propagating in the VBC fiber using an acoustic wave. Theperturbation is caused by the modification of the refractive index ofthe fiber by the oscillating mechanical pressure of an acoustic wave.The period and strength of the acoustic wave are related to the acousticwave frequency and amplitude, allowing dynamic control of the acousticperturbation. Thus, a perturbation assembly 110 including AOT 2408 maybe configured to vary the beam characteristics of a beam propagating inthe fiber. In an example, a piezo-electric transducer 2418 may createthe acoustic wave and may be controlled by a controller or driver 2420.The acoustic wave induced in AOT 2408 may be modulated to change and/orcontrol the beam characteristics of the optical beam in VBC 200 inreal-time. However, this is merely an example of a method for creatingand controlling an AOT 2408, and claimed subject matter is not limitedin this regard.

Thermal device 2410 may be used to induce perturbation of a beampropagating in VBC fiber using heat. The perturbation is caused by themodification of the RIP of the fiber induced by heat. Perturbation maybe dynamically controlled by controlling an amount of heat transferredto the fiber and the length over which the heat is applied. Thus, aperturbation assembly 110 including thermal device 2410 may beconfigured to vary a range of beam characteristics. Thermal device 2410may be controlled by a controller 2450.

Piezo-electric transducer 2412 may be used to induce perturbation of abeam propagating in a VBC fiber using piezoelectric action. Theperturbation is caused by the modification of the RIP of the fiberinduced by a piezoelectric material attached to the fiber. Thepiezoelectric material in the form of a jacket around the bare fiber mayapply tension or compression to the fiber, modifying its refractiveindex via the resulting changes in density. Perturbation may bedynamically controlled by controlling a voltage to the piezo-electricdevice 2412. Thus, a perturbation assembly 110 including piezo-electrictransducer 2412 may be configured to vary the beam characteristics overa particular range.

In an example, piezo-electric transducer 2412 may be configured todisplace VBC fiber 200 in a variety of directions (e.g., axially,radially, and/or laterally) depending on a variety of factors, includinghow the piezo-electric transducer 2412 is attached to VBC fiber 200, thedirection of the polarization of the piezo-electric materials, theapplied voltage, etc. Additionally, bending of VBC fiber 200 is possibleusing the piezo-electric transducer 2412. For example, driving a lengthof piezo-electric material having multiple segments comprising opposingelectrodes can cause a piezoelectric transducer 2412 to bend in alateral direction. Voltage applied to piezoelectric transducer 2412 byan electrode 2424 may be controlled by a controller 2422 to controldisplacement of VBC fiber 200. Displacement may be modulated to changeand/or control the beam characteristics of the optical beam in VBC 200in real-time. However, this is merely an example of a method ofcontrolling displacement of a VBC fiber 200 using a piezo-electrictransducer 2412 and claimed subject matter is not limited in thisregard.

Gratings 2414 may be used to induce perturbation of a beam propagatingin a VBC fiber 200. A grating 2414 can be written into a fiber byinscribing a periodic variation of the refractive index into the core.Gratings 2414 such as fiber Bragg gratings can operate as opticalfilters or as reflectors. A long-period grating can induce transitionsamong co-propagating fiber modes. The radiance, intensity profile,and/or divergence profile of a beam comprised of one or more modes canthus be adjusted using a long-period grating to couple one or more ofthe original modes to one or more different modes having differentradiance and/or divergence profiles. Adjustment is achieved by varyingthe periodicity or amplitude of the refractive index grating. Methodssuch as varying the temperature, bend radius, and/or length (e.g.,stretching) of the fiber Bragg grating can be used for such adjustment.VBC fiber 200 having gratings 2414 may be coupled to a stage 2426. Stage2426 may be configured to execute any of a variety of functions and maybe controlled by a controller 2428. For example, stage 2426 may becoupled to VBC fiber 200 with fasteners 2430 and may be configured tostretch and/or bend VBC fiber 200 using fasteners 2430 for leverage.Stage 2426 may have an embedded thermal device and may change thetemperature of VBC fiber 200.

FIG. 25 illustrates an example process 2500 for adjusting and/ormaintaining beam characteristics within a fiber without the use offree-space optics to adjust the beam characteristics. In block 2502, afirst length of fiber and/or an optical beam are perturbed to adjust oneor more optical beam characteristics. Process 2500 moves to block 2504,where the optical beam is launched into a second length of fiber.Process 2500 moves to block 2506, where the optical beam having theadjusted beam characteristics is propagated in the second length offiber. Process 2500 moves to block 2508, where at least a portion of theone or more beam characteristics of the optical beam are maintainedwithin one or more confinement regions of the second length of fiber.The first and second lengths of fiber may be comprised of the samefiber, or they may be different fibers.

FIG. 29 shows a beam shaper system 2900 implemented with an optical beamdelivery device 2902 in the form of a VBC fiber 2906, which isconstructed in accordance with the disclosed paradigm represented byexample VBC fiber 100 (see e.g., FIG. 1 for additional details). Forconciseness, some previously described details of FIG. 1 are furthersimplified and, therefore, not reproduced in FIG. 29. Note also thatsubscripts “A,” “B,” “C,” and “D” represent different selectableconfigurations of beam shaper system 2900, which are explained in thefollowing paragraphs.

A laser source 2910 emits optical beam 102 (FIG. 1) propagating in afirst length of fiber 2912, which corresponds to first length of fiber104 (FIG. 1). Optical beam 102 is incident on VBC fiber 2906.Perturbation device 110 operating in combination with, and applyingdifferent states (e.g., different amounts or directions) of perturbationto, VBC fiber 2906 directs the fiber mode to different correspondingconfinement regions of a second length of fiber 2920, which correspondsto second length of fiber 108 (FIG. 1).

As described previously with reference to FIG. 24, a controller 2930enables beam shaper system 2900 to selectively move the fiber mode,i.e., the intensity distribution, of optical beam 102 to different areasat an input of second length of fiber 2920. In some embodiments,controller 2930 comprises a computer workstation having input-output(I/O) devices suitable for establishing a signal interface withperturbation device 110 so as to signal states of perturbation thatcorrespond to desired beam shapes indicated through, e.g., user input.Skilled persons will appreciate that controller 2930 may include acentral processing unit (CPU), field-programmable gate array (FPGA), orother control devices suitable for performing logic operations.Controller 2930 may also include a non-transitory machine readablestorage medium storing instructions thereon that, when executed, causecontroller 2930 to perform any methods or operations described in thisdisclosure.

In a first “A” configuration, controller 2930 signals perturbationdevice 110 to apply a first state of perturbation to VBC fiber 2906 andthereby establish a first selected intensity profile 2940 _(A) at anoutput end of second length of fiber 2920. An output beam having firstselected intensity profile 2940 _(A) is then delivered by a process head2950 to a workpiece 2960.

In a subsequent “B” configuration, controller 2930 signals perturbationdevice 110 to apply a second state of perturbation, different from thefirst state, to VBC fiber 2906 and thereby establish a second selectedintensity profile 2940 _(B), different from first selected intensityprofile 2940 _(A), at the output end of second length of fiber 2920.Thus, perturbation device 110, in response to control signals fromcontroller 2930, applies to VBC fiber 2906 a selected amount ordirection of bend that shifts the fiber mode to a different area ofconfinement regions (c.f., different areas shown in FIGS. 7A, 8A, 9A,and 10A) and thereby provides a means of establishing, at an output ofsecond length of fiber 2920, different selectable intensity profiles2970.

Different intensity profiles 2970 are selectable based on differentmaterial properties. According to some embodiments, a change from oneperturbation state to another state is configured indirectly, e.g., inresponse to a selected change 2980 in either a type of material to beprocessed or an indirectly related calibration setting for material ofthe same or different types than that of workpiece 2960. In otherembodiments, a change from one perturbation state to another state isconfigured directly, e.g., by a direct selection 2990 of a desired beamshape (i.e., potentially irrespective of material). Thus, a user maysimply select a material or a beam shape through a selection interface2996 provided by, e.g., controller 2930, so as to dynamically changebeam shape. The change may also be made fully or partly autonomously.For conciseness, a resulting intensity profile selected directly orindirectly is simply referred to as a selected intensity profile.Furthermore, skilled persons will appreciate that a selection of anintensity distribution is equivalent to a selection of an intensityprofile—particularly since, in an azimuthally symmetric set ofconfinement regions, a given intensity profile is generally the sameacross any radial cross-sectional position among of the set ofconfinement regions.

Having described and illustrated the general and specific principles ofexamples of the presently disclosed technology, it should be apparentthat the examples may be modified in arrangement and detail withoutdeparting from such principles. We claim all modifications and variationcoming within the spirit and scope of the following claims.

1. An optical beam delivery device configured to generate, from anoptical beam, selectable intensity profiles, the optical beam deliverydevice comprising: a first length of fiber having a first refractiveindex profile (RIP), the first RIP enabling, in response to an appliedperturbation, modification of the optical beam to form an adjustedoptical beam, the adjusted optical beam defining, at an output end ofthe first length of fiber, different intensity distributions based ondifferent states of the applied perturbation; and a second length offiber having an input end coupled to the output end of the first lengthof fiber, the second length of fiber formed with coaxial confinementregions defining a second RIP that is different from the first RIP, thecoaxial confinement regions arranged to confine at least a portion ofthe adjusted optical beam, the confined portion corresponding to anintensity distribution of the different intensity distributions, and inwhich the intensity distribution is established by a corresponding stateof the different states of the applied perturbation such that theconfined portion is configured to provide, at an output of the secondlength of fiber, a selected intensity profile of the selectableintensity profiles.
 2. The optical beam delivery device of claim 1, inwhich the selected intensity profile is a Gaussian intensity profile. 3.The optical beam delivery device of claim 2, in which the correspondingstate of the different states of the applied perturbation establishingthe Gaussian intensity profile includes an unperturbed state of thefirst length of fiber.
 4. The optical beam delivery device of claim 2,in which a central core of the coaxial confinement regions is configuredto provide the confined portion having the Gaussian intensity profile.5. The optical beam delivery device of claim 1, in which the selectedintensity profile is a super-Gaussian intensity profile.
 6. The opticalbeam delivery device of claim 1, in which the coaxial confinementregions comprise a central core and an annular region encompassing thecentral core, and in which the corresponding state of the differentstates of the applied perturbation is that which shifts, expands, orsimultaneously shifts and expands the optical beam in forming theadjusted optical beam so that the intensity distribution which resultsat the input of the second length of fiber spatially overlaps adjacentportions of the central core and the annular region.
 7. The optical beamdelivery device of claim 1, in which the selected intensity profile is aflat-top intensity profile.
 8. The optical beam delivery device of claim1, in which the selected intensity profile is a saddle-shaped intensityprofile.
 9. The optical beam delivery device of claim 1, in which thecoaxial confinement regions comprise a central core and an annularregion encompassing the central core, and in which the intensitydistribution spatially overlaps an outer portion of the central core andan inner portion of the annular region.
 10. The optical beam deliverydevice of claim 1, in which the selected intensity profile is adonut-shaped intensity profile.
 11. The optical beam delivery device ofclaim 1, in which the selected intensity profile includes a localminimum between bimodal local maxima.
 12. A beam shaper system,comprising: a laser source to provide an optical beam; a variable beamcharacteristics (VBC) fiber including first and second lengths of fibercoupled to each other and having, respectively, first and secondrefractive index profiles (RIPs) that are different from each other, thefirst RIP enabling, in response to perturbation applied to the VBCfiber, modification of the optical beam to form an adjusted optical beamexhibiting at an input of the second length of fiber an intensitydistribution that is adjustable based on different states of theperturbation applied, and the second RIP defined by coaxial confinementregions arranged to confine at least a portion of the adjusted opticalbeam that corresponds to the intensity distribution; and a controlleroperatively coupled to the VBC fiber and configured to control thedifferent states of the perturbation so as to establish differentselectable intensity profiles that the confined portion of the adjustedoptical beam is configured to provide at an output of the second lengthof fiber.
 13. The beam shaper system of claim 12, in which one of thedifferent selectable intensity profiles is a Gaussian intensity profile.14. The beam shaper system of claim 12, in which one of the differentselectable intensity profiles is a super-Gaussian intensity profile. 15.The beam shaper system of claim 12, in which one of the differentselectable intensity profiles is a saddle-shaped intensity profile. 16.The beam shaper system of claim 12, in which one of the differentselectable intensity profiles is a donut-shaped intensity profile.
 17. Amethod of generating, from an optical beam, different beam shapesdefined by selectable intensity profiles, comprising: receiving theoptical beam at a variable beam characteristics (VBC) fiber includingfirst and second lengths of fiber coupled to each other and having,respectively, first and second refractive index profiles (RIPs) that aredifferent from each other, the first RIP enabling, in response to aselected state of perturbation applied to the VBC fiber, modification ofthe optical beam to form an adjusted optical beam that is adjustablebased on the selected state of applied perturbation, and the second RIPdefined by coaxial confinement regions arranged to confine at least aportion of the adjusted optical beam; applying a first state ofperturbation to the VBC fiber to establish a first selected intensityprofile at an output end of the second length of fiber; and applying asecond state of perturbation, different from the first state, to the VBCfiber to establish a second selected intensity profile, different fromthe first selected intensity profile, at the output end of the secondlength of fiber.
 18. The method of claim 17, in which the first selectedintensity profile is a generally Gaussian intensity profile, and thesecond intensity profile is a generally super-Gaussian profile.
 19. Themethod of claim 17, in which the second state of perturbation is amagnitude of perturbation that is greater than that of the first state.20. The method of claim 17, in which the first selected intensityprofile is a generally saddle-shaped intensity profile, and the secondintensity profile is a generally donut-shaped intensity profile.